docs: def createCells(self):
          '''Function to instantiate Cell objects based on the characteristics of this population'''
          # add individual cells
          if 'cellsList' in self.tags:
              cells = self.createCellsList()
  
          # create cells based on fixed number of cells
          elif 'numCells' in self.tags:
              cells = self.createCellsFixedNum()
  
          # create cells based on density (optional ynorm-dep)
          elif 'density' in self.tags:
              cells = self.createCellsDensity()
  
          # create cells based on density (optional ynorm-dep)
          elif 'gridSpacing' in self.tags:
              cells = self.createCellsGrid()
  
          # not enough tags to create cells
          else:
              self.tags['numCells'] = 1
              print('Warninig: number or density of cells not specified for population %s; defaulting to numCells = 1' % (self.tags['pop']))
              cells = self.createCellsFixedNum()
  
          return cells